Add some comments on .gitlab-ci.yml

.gitlab-ci.yml

@@ -13,7 +13,7 @@ build:
   variables:
       GIT_SUBMODULE_STRATEGY: normal
       GCC_COLORS: "error=31;1:warning=35;1:note=36;1:range1=32:range2=34:locus=39;1:quote=39;1:fixit-insert=32:fixit-delete=31:diff-filename=39;1:diff-hunk=32:diff-delete=31:diff-insert=32:type-diff=32;1"
-      CLICOLOR_FORCE: 1
+      CLICOLOR_FORCE: 1 # Necessary for cmake to output colours
   script:
     - cmake . -DCMAKE_CXX_FLAGS="-Werror -fdiagnostics-color=always"
     - make -j4
@@ -58,8 +58,10 @@ clang-tidy:
     GIT_SUBMODULE_STRATEGY: normal
     TERM: xterm-color
   before_script:
+    # Installing the `sid` repository to get the latest version of clang
     - echo deb http://deb.debian.org/debian sid main > /etc/apt/sources.list
     - apt-get update -qq && apt-get -t sid install -y -qq clang-tidy-7
     - clang-tidy-7 --version
   script:
+    # Running with `script` to give clang a tty so that it outputs colours
     - script -c "bash -x ci/clang-tidy.sh"